Improved manufacturing techniques, customer sophistication, and rising labor costs continue to engender developments in emergency lighting. Conventional emergency lighting fixture housings have been connected to their canopies (which in turn are mounted to junction boxes or other structure within or on a wall, ceiling or other surface) using elongated threaded metal conduit with retaining nuts. That structure, which is similar to the threaded conduit used in other lighting fixtures such as ceiling and lamp fixtures, is characteristically difficult and time consuming to install. Furthermore, pliers or other tools must be employed to torque the nut that secures the housing to the canopy. A secure fit is important because the emergency lighting must remain in place for many years with minimum risk of failure. Among other things, relative movement between the canopy and the housing can, over time, subject wiring and insulation to cyclical stresses which, when combined with temperature excursions, can create failure of the wiring and/or the insulation to create either an open circuit or a short and thus failure of the emergency lighting.
Recent developments include emergency lighting in which the canopies feature mounting posts that in turn contain barbs or snaps which protrude into the housings, snap into place and retain the housings against the canopies. Such retention may be made secure if the housing body is caused to flex against certain structure of the canopy, although stresses induced in the housing structure from such flexion may be exacerbated over time if the fixture is subjected to undue temperature excursions and/or vibration. Furthermore, a typical housing usually contains batteries for emergency backup lighting, as well as transformers, and thus can impose considerable load on the small snap surface area which retains the housing aloft. Nevertheless, such snap fittings are advantageous to the extent that they eliminate the need for installation tools and thus save installation time, effort and expense.